The present invention generally relates to a fuel pump for a fuel-injected engine in an automotive vehicle and more particularly relates to the reduction of radio frequency interference (RFI) from an electric fuel pump motor situated within a fuel pump housing.
Modernly, various different electrical and electronic systems with increased levels of complexity and sophistication are being incorporated in many automotive vehicles. Whereas some of these systems are generally unaffected by and will even sometimes themselves generate stray electromagnetic wave interference (EMI) or radio frequency interference (RFI) (i.e., xe2x80x9cnoisexe2x80x9d) during operation, others of these systems need to be protected from such noise in order to function and operate properly. For example, many of the audio systems that are onboard many modem vehicles include highly sophisticated electronics that help ensure high-fidelity sound reproduction. Typically, such audio systems are electrically sensitive and are often adversely affected during operation when exposed to significant amounts of stray noise. Similarly, electronically sophisticated onboard communication systems such as, for example, two-way radios, cellular telephones, and GPS (global positioning satellite) navigational systems are also often adversely affected during operation when exposed to certain amounts of stray noise.
An electric fuel pump motor commonly situated within the housing of a fuel pump for an automotive vehicle is often a significant source of stray noise. Such is particularly true while the electric motor is operating and thereby enabling the fuel pump to successfully draw fuel from a fuel tank and thereafter deliver the fuel under pressure to an engine. For example, when connected to an electrical power source, the electric motor may utilize one or more energized coils or solenoids to operate the fuel pump. In doing so, as the level of electric current conducted through the coils is varied to correspondingly vary the speed of the fuel pump to satisfy the ever-changing fuel needs of the engine, an electromagnetic field with an ever-changing field strength is thereby generated about the coils. This generated electromagnetic field also emanates in the form of a wave and strays from the immediate vicinity of the coils as undesirable noise. Depending on the field strength and the characteristic frequency of the noise, as dictated by the changes in its field strength, the noise may interfere with the electrical signals of sensitive electronic systems that are situated outside of and about the fuel pump housing. As a result, operation of these electronic systems may be adversely affected. As another example, when connected to an electrical power source, xe2x80x9cpositivexe2x80x9d and xe2x80x9cnegativexe2x80x9d brushes which are in electrical and mechanical sliding contact with and conduct electric current to the rotatable commutator of the electric fuel pump motor may cause xe2x80x9cbrush firingxe2x80x9d as the commutator rotates. Such brush firing can generate stray noise that too may adversely affect the operation of electronic systems outside of and about the fuel pump housing. Furthermore, in addition to these two particular examples, other sources of stray noise directly or indirectly associated with the operation of the electric motor are possible as well.
In an attempt to reduce the amount of stray noise directly or indirectly emanating from or associated with the electric fuel pump motor, remedial electric circuits sometimes referred to as xe2x80x9cradio frequency interference (RFI) suppression circuitsxe2x80x9d or xe2x80x9cradio frequency noise suppression circuitsxe2x80x9d have been proposed. Such circuits are typically interconnected between an outside electrical power source and the electric motor. These circuits typically include two choke coils and a capacitor. In particular, one choke coil is electrically connected between the positive terminal of the electrical power source and the positive brush, and the other choke coil is electrically connected between the negative terminal of the electrical power source and the negative brush. The capacitor is electrically connected between corresponding ends of the two choke coils. These circuits are typically situated or mounted on the fuel outlet end of the fuel pump housing. See, for example, U.S. Pat. No. 4,845,393, issued to Burgess et al on Jul. 4, 1989, U.S. Pat. No. 5,697,769, issued to Kobman et al on Dec. 16, 1997, and U.S. Pat. No. 5,734,212, issued to Uffelman on Mar. 31, 1998.
Although such remedial circuits do attain some measure of success in reducing stray noise associated with electric fuel pump motors, such circuits alone, however, sometimes fall short in reducing noise to the extent necessary to prevent increasingly sensitive modern electronic systems from being adversely affected during operation. In light of such, there is a present need in the art for a device, structure, or system that will further reduce, either alone or in conjunction with such remedial circuits, the amount of stray noise associated with electric fuel pump motors.
The present invention provides a shield structure for reducing radio frequency interference (RFI) from an electric motor situated within a fuel pump housing. The shield structure is ideal for a fuel pump housing that has an end having a fuel inlet and another end having a fuel outlet. According to the present invention, the shield structure basically includes, first of all, an electrically insulative and hollow cup-like outer cover mountable on the fuel outlet end of a fuel pump housing. The outer cover has an inner surface, an outer surface, and, in a preferred embodiment, a fuel outlet opening defined therethrough. In addition, the shield structure also basically includes an electrically conductive outer coat layer formed on substantially all of the outer surface of the outer cover. Furthermore, the shield structure also basically includes means for electrically grounding the outer coat layer to the electric motor of the fuel pump housing.
In a preferred embodiment of the present invention, the outer cover comprises plastic, and the outer coat layer comprises silver. In a highly preferred embodiment, the outer coat layer comprises both silver-plated copper and an acrylic binder. Furthermore, the outer coat layer preferably has a minimum thickness of about 0.010 millimeters and more preferably has a minimum thickness of about 0.012 millimeters.
Also, in a preferred embodiment of the present invention, the shield structure further includes a fuel outlet conduit and two open-ended cylindrical retainer chambers. The fuel outlet conduit is preferably integral with both the inner surface and the outer surface of the outer cover such that the fuel outlet conduit defines the fuel outlet opening through both the outer cover and the outer coat layer. The two open-ended cylindrical retainer chambers are preferably defined through both the outer cover and the outer coat layer.
Further, in a preferred embodiment of the present invention, the shield structure further includes a fuel relief conduit. The fuel relief conduit is preferably integral with the inner surface of the outer cover such that the fuel relief conduit defines a fuel relief opening through both the outer cover and the outer coat layer. The fuel relief conduit is preferably tapered for thereby accommodating and seating a fuel relief ball valve.
Still further, in a preferred embodiment of the present invention, the shield structure further includes two electrical conduits. The two electrical conduits are preferably integral with the inner surface of the outer cover such that the two electrical conduits define two electrical conduit openings through both the outer cover and the outer coat layer. The outer coat layer preferably has discontinuities on the outer surface of the outer cover such that the outer coat layer is radially spaced away from each of the two electrical conduit openings on the outer surface. In such a configuration, the two electrical conduits are capable of closely receiving two electrically conductive pins for communicating electric power to the electric motor in such a way that the two electrically conductive pins are electrically isolated from said outer coat layer.
Lastly, in a preferred embodiment of the present invention, the electrical grounding means includes both an electrical ground conduit and an electrically conductive inner coat layer formed on the inner surface of the electrical ground conduit. The electrical ground conduit is preferably integral with the inner surface of the outer cover such that the electrical ground conduit defines an electrical ground opening through both the outer cover and the outer coat layer. The inner coat layer formed on the inner surface of the electrical ground conduit is preferably conterminous with the outer coat layer formed on the outer surface of the outer cover.
Objects, features, and advantages of this invention include providing a shield structure which is capable of further reducing the amount of stray noise associated with electric fuel pump motors as well as providing a shield structure which is compact, rugged, durable, of relatively simple design and economical manufacture and assembly, and has a long useful life in service.